1. Field of the Invention
The invention relates to a method of manufacture particularly applicable to turbine rings comprising a ceramic elment rigid with an annular metallic carrier.
2. Summary of the Prior Art
The advantages of the use of ceramic materials for forming fluidtight stator rings of a turbine disposed opposite to the rotor of one stage of the turbine are well known. The low thermal conductivity of these materials enables, in practice, a remarkable effectiveness as a thermal barrier and their use thus enables construction of stator elements, in particular of the casings, such that they respond more readily to other requirements of their operation, of low cost and with easy practical application. The good resistance of ceramic materials to high temperatures enables in particular reduction or under certain circumstances omission of all cooling and to thus reduce the cooling air flow, which enables appreciable gains in efficiency. These materials also have corrosion resistance properties when hot which are advantageous in turbine rings.
Nevertheless, the extension of the use of ceramic materials to turbine rings has been retarded by various constraints based on dificulties in putting into practice ceramic materials in these applications. Ceramic materials, especially when heavy, compact, types are concerned have a poor strength when they are submitted to tensile forces. Moreover, their low coefficient of thermal expansion give rise to serious operational problems in their connections with metallic carriers. Several prior proposals have aimed at resolving these problems.
FR-A-2 371 575 describes a turbine ring in which a ceramic ring is built up by juxtaposition of segments. This proposal, however, necessitates manufacturing and assembly method which are relatively complicated and hence costly. Furthermore, inevitable discontinuities, in the region of the coupled edges of the segments are prejudicial to satisfactory gas flow.
An improvement described by FR-A-2 540 938 provides for resilient securing of the ceramic segments to a ring by one bolt of which the head transmits to the segment an axial force which applies it against the ring.
FR-A-2 559 834 provides for the use of a ceramic ring in one piece, which enables avoidance of several of the disadvantages hereinbefore referred to. The mounting method proposed in the zone of an annular carrier of wound ceramic material, enables a compressive pre-stress of the ceramic ring but is not however entirely satisfactory in all applications.